Bristle rotifer
Polyarthra vulgaris
The bristle rotifer of the genus Polyarthra is a widespread inhabitant of limnic zooplankton. It is characterized by distinctive, sword-shaped appendages that function as fins or bristles, enabling lightning-fast jumping reactions when threatened. These microscopic animals are usually transparent and possess a complex corona for food intake. They play a central role in the aquatic food web as consumers of phytoplankton and bacteria. In many lakes, they are among the most common rotifer species.
Details
Identification
Sac-shaped body; four bundles of three sword-shaped appendages (fins) each; no foot present; clearly visible corona (ciliated organ).
Social behavior
Solitary floating in open water, but can form mass developments under favorable conditions.
Diet
Primarily herbivorous; feeds on small algae (e.g., cryptomonads) and organic particles swirled in by the corona.
Hunting strategy
Filter feeder; uses the beating cilia of the corona to create a feeding current.
Overwintering
Formation of thick-walled resting eggs (diapause stage) that survive unfavorable conditions at the bottom of the water body.
Ecology
Ecological role
Important primary consumer transferring energy from phytoplankton to higher trophic levels such as predatory zooplankton and fish larvae.
Natural predators
Other predatory rotifers (e.g., Asplanchna), copepods, and planktivorous juvenile fish.
Competitor species
Other rotifer genera such as Keratella or Brachionus, as well as filtering water fleas (Daphnia).
Ecosystem service
Regulation of algal growth and contribution to the self-purification of water bodies.
Threats
Water pollution by toxins, extreme acidification, and invasive predatory species.
Scientific profile
Profile
Distinguishing features
Possesses 12 leaf- or sword-shaped appendages (setae) that can be longer than the body, used for sudden escape jumps. A foot is entirely absent. The mastax is of the virgate type, used for sucking out prey. Vitellaria usually contain eight nuclei.
Reproduction
Heterogony: For most of the year, reproduction is parthenogenetic (amictic). Under stress conditions (food shortage, population density), mictic females appear, which produce resting eggs after fertilization.
Role in food web
Central primary consumer in the pelagic zone; transfers energy from nanoplankton (microbial loop) to higher trophic levels.
Protection & threats
Status not on standard scale
Main threats
No immediate threats known; potential impairment through extreme acidification or heavy toxic loads (pesticides) in agricultural landscapes.